rates of reactions

Question 1

What is the rate equation

Answer 1

Rate = k [A]^x[B]^y , where A and B are reactants

Question 2

What are the units for rate

Answer 2

Usually moldm-3 however can be units on y axis / units on x axis -1

Question 3

What is an order of reaction

Answer 3

In a reaction , different reactants have different orders and each will effect the rate of reaction differently . Zero order will not have an effect on rate , 1 st order will have a proportional effect on rate , and 2nd order will have a squared effect on rate

Question 4

How do you state what order a reactant is

Answer 4

• a reaction is ………. Order with respect to [X]

Question 5

How do you work out the overall order of a reaction

Answer 5

Add the powers

Question 6

What are the different ways rate can be measured

Answer 6

• change in PH of a reaction , eg if H+ ions are used up or produced
  -amount of mass lost (gas being produced)
  -volume of gas produced
  -colorimeter - measures the absorbance of light , the more concentrated , the more pigment and the more light absorbed
  -

Question 7

What is the rate constant

Answer 7

The rate constant K , allows us to equate rate and concentration

Question 8

What happens with K

Answer 8

k is only fixed at a particular temperature , if temperature changes so does the rate constant . K increases when temperature increases . The larger the value of ‘k’ the faster the rate of reaction
Because particles have more kinetic energy and frequency of collisions increases
- concentrations of substances remain constant so k must change .

Question 9

How do you find the units and value for k

Answer 9

• through experimental data find the rate equation
• rearrange for k and sub in units
• use experimental data to sub in values to find the rate constant